Laser diode driver, method of driving the laser diode driver, and method of initializing an optical recording and reproducing apparatus

ABSTRACT

A laser diode (LD) driver and method of compensating for a bias driving potential of an LD driver according to a change in a power level of a laser signal from an LD in a recording mode include storing the bias driving potential, detecting a change in a bias power level in the laser signal, and compensating the bias driving potential according to the detected change in the bias power level.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.09/775,678, filed Feb. 5, 2001, now U.S. pat. No. 6,738,339 allowed.

This application is based upon and claims the priority of Japaneseapplication no. 2000-5487, filed Feb. 3, 2000, and U.S. patentapplication Ser. No. 10/189,197, filed 09/775,678, filed Feb. 5, 2001,the contents being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser diode (LD) driver for drivingan LD in an optical recording and reproducing apparatus, and moreparticularly, to an apparatus, which has an auto laser power control(ALPC) function and can drive two or more LDs using the LD driver, amethod of driving the LD driver, and a method of initializing theoptical recording and reproducing apparatus.

2. Description of the Related Art

FIG. 1 illustrates the structure of a laser diode (LD) driver 100 fordriving an LD (not shown) currently used in optical recordingapparatuses.

The components of the LD driver 100 include switches 10 a through 10 c,a multiplexer 12 for multiplexing the outputs of the switches 10 athrough 10 c, an amplifier 14 for amplifying the output of themultiplexer 12 with a predetermined degree of amplification, an adder16, and a high frequency modulator (HFM) 18.

Current such as peak current, bias current, and read current, or voltagecorrespond to power levels such as peak power level, bias or erase powerlevel, and read power level of the LD, which are applied to the switches10 a through 10 c. The power levels are turned on and off by controlsignals such as peak control, bias control, and read control.

The outputs of the switches 10 a through 10 c are multiplexed by themultiplexer 12. The output of the multiplexer 12 is applied to arecording medium. Because the LD cannot be fully driven by the output ofthe multiplexer 12 alone, the output of the multiplexer 12 is amplifiedthrough the amplifier 14.

The HFM 18 generates a high frequency modulation signal to removeoptical interference noise from an optical pick-up (not shown). Theadder 16 adds the high frequency modulation signal to the output of theamplifier 14 and outputs a driving signal to the LD. The LD, in turn,generates a recording signal corresponding to the driving signal fromthe adder 16. Here, the high frequency modulation signal is set to havethe most effective frequency and magnitude for removing the opticalinterference noise and is primarily used in a read mode. Further, in theLD driver 100, the number of switches may include two to five switchesaccording to the number of channels used (2ch through 5ch), which arethe number of driving levels in a recording signal.

The LD changes according to an operating temperature. Specifically,referring to FIG. 2, an output characteristic of TOLD9452MB, which is anLD driver by Toshiba Co., Ltd. is illustrated. Here, when the LD isoperating and a constant input current is applied, the operatingtemperature increases and the optical output decreases. For example,when an input current of 110 mA is applied, the optical output isreduced from 40 mW at 25° C. to about 20 mW at 70° C. The reduction ofthe optical output causes a recording function to either deteriorate ornot be able to be performed.

To improve such reduction, conventional LD drivers use an automaticlaser diode power control (ALPC). In the ALPC, the output of the LD ismonitored through an additional monitor diode and the change in theoutput of the LD is fed back. Accordingly, the output of the LD ismaintained uniform. However, the ALPC function cannot be realized onlyby the LD driver, but it must be realized by an additional circuit or anintegrated circuit (IC). Accordingly, electromagnetic wave interferencemay cause mis-operation during an interface operation when supplying theLD output control signal provided by the ALPC to the LD driver.Furthermore, when recording speed increases, the interface operation maynot be performed. The waveform of the LD is reduced to either 780 μm (inthe case of a CD), 635 or 650 μm (in the case of a DVD), or 410 μm as aresult of development of recording technology and increase in capacity.If a recording and reproducing apparatus includes a plurality of LDs,which lower compatibility and share between a recording medium, multiplecircuit blocks for the ALPC corresponding to the respective LDs arenecessary. Accordingly, a plurality of circuit blocks performing similaroperations must be included. This is a big obstacle to making productssmall, light, and inexpensive.

SUMMARY OF THE INVENTION

Various objects and advantages of the invention will be set forth inpart in the description which follows and, in part, will be obvious fromthe description, or may be learned by practice of the invention.

The present invention is achieved by providing an objective lens forhigh-density focusing. The objective lens is a single lens having a highnumerical aperture (NA). The objective lens is included in an opticalpickup that also includes a relatively thin optical disk.

Accordingly, it is an object of the present invention to provide anapparatus and method including switches turning on and off drivingpotentials, each switch corresponding to the power level of the lasersignal according to the channel control signals. A multiplexermultiplexes the driving potentials and outputs a multiplexed signal. Amonitor diode monitors the power level of the laser signal and outputs amonitor signal. Further, a sample and hold unit samples and holds themonitor signal and outputs a signal indicative thereof. A differentialamplifier calculates a difference between a reference signalcorresponding to the power level of the laser signal and the outputsignal from the sample and hold unit. An adder adds the difference andthe multiplexed signal and outputs therefrom a driving signal to drivethe LD.

Furthermore, it is another object of the present invention to providefor a method receiving channel control signals to control differentpower levels of a laser signal from the LD; turning on and off drivingpotentials corresponding to the power level of the laser signalaccording to the channel control signals; multiplexing the drivingpotentials and outputting a multiplexed signal; monitoring the powerlevel of the laser signal and outputting a monitor signal; sampling andholding the monitor signal and outputting a signal indicative thereof;calculating a difference between a reference signal corresponding to thepower level of the laser signal and the output signal from the samplingand holding; and adding the difference and the multiplexed signal andoutputting therefrom a driving signal to drive the LD.

Furthermore, it is another object of the present invention to providefor a method of driving an LD, including determining a type of a loadedrecording medium; and setting driving potentials corresponding to powerlevels of a laser signal output from the LD according to the determinedtype of the recording medium.

Furthermore, it is another object of the present invention to providefor a method of compensating for a bias driving potential of an LDdriver according to a change in a power level of a laser signal from anLD in a recording mode, including storing the bias driving potential;detecting a change in a bias power level in the laser signal; andcompensating the bias driving potential according to the detected changein the bias power level.

These together with other objects and advantages which will besubsequently apparent, reside in the details of construction andoperation as more fully hereinafter described and claimed, referencebeing had to the accompanying drawings forming a part hereof, whereinlike numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

The various objects and advantages of the present invention will becomeapparent and more readily appreciated from the following description ofthe preferred embodiments, taken in conjunction with the accompanyingdrawings of which:

FIG. 1 is a diagram illustrating a structure of a conventional laserdiode (LD) driver;

FIG. 2 is a graph illustrating an output characteristic of a LD;

FIG. 3 is a diagram illustrating an LD driver, in accordance with anexemplary embodiment of the present invention;

FIG. 4A(a) illustrates a waveform of an input NRZI data for recording ina CD-RW;

FIG. 4A(b) illustrates a waveform of a recording waveform (LD outputsignal) for recording in the CD-RW;

FIG. 4A(c) illustrates a waveform of a read control (active) signal forrecording in the CD-RW;

FIG. 4A(d) illustrates a waveform of a peak control signal for recordingin the CD-RW;

FIG. 4A(e) illustrates a waveform of a bias 1 control signal (erasepower) for recording in the CD-RW;

FIG. 4A(f) illustrates a waveform of a bottom (base 3) control signal(when four channels are used) for recording in the CD-RW;

FIG. 4B(a) illustrates a waveform of an input NRZI data for recording ina DVD-RAM;

FIG. 4B(b) illustrates a waveform of a recording waveform (LD outputsignal) for recording in the DVD-RAM;

FIG. 4B(c) illustrates a waveform of a peak control signal (write level)for recording in the DVD-RAM;

FIG. 4B(d) illustrates a waveform of a bias 1 control signal (eraselevel) for recording in the DVD-RAM;

FIG. 4B(e) illustrates a waveform of a bias 2 control signal (bottomlevel) for recording in the DVD-RAM;

FIG. 4B(f) illustrates a waveform of a bias 2 control signal and bias 3control signal for recording in the DVD-RAM;

FIG. 4B(g) illustrates a waveform of a bias 3 control signal (coolinglevel) for recording in the DVD-RAM;

FIG. 4B(h) illustrates a waveform of a read control signal (active) forrecording in the DVD-RAM;

FIG. 5( a) illustrates a waveform of an example of inputting NRZIdescribing the sampling operation of the sample and hold circuit in theLD driver of FIG. 3;

FIG. 5( b) illustrates a waveform of bias 1 control signal (example ofhigh active) describing the sampling operation of the sample and holdcircuit in the LD driver of FIG. 3;

FIG. 5( c) illustrates a waveform of a primary delay signal of bias 1describing the sampling operation of the sample and hold circuit in theLD driver of FIG. 3;

FIG. 5( d) illustrates a waveform of a secondary delay signal of bias 1describing the sampling operation of the sample and hold circuit in theLD driver of FIG. 3;

FIG. 5( e) illustrates a waveform of a tertiary delay signal of bias 1describing the sampling operation of the sample and hold circuit in theLD driver of FIG. 3;

FIG. 5( f) illustrates a waveform of a sampling and holding signal 1 ofbias 1 describing the sampling operation of the sample and hold circuitin the LD driver of FIG. 3;

FIG. 5( g) illustrates a waveform of a sampling and holding signal 2 ofbias 1 describing the sampling operation of the sample and hold circuitin the LD driver of FIG. 3;

FIG. 5( h) illustrates a waveform of a sampling and holding signal 3 ofbias 1 describing the sampling operation of the sample and hold circuitin the LD driver of FIG. 3; and

FIG. 6A and FIG. 6B are flowcharts illustrating initializing and drivingmethods, in accordance with an exemplary embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the structure and operation of the present invention willbe described in detail with reference to the attached drawings.

FIG. 3 is a diagram illustrating a structure of a laser diode (LD)driver 200, in accordance with an exemplary embodiment of the presentinvention. The components of the LD driver 200 that perform the sameoperations as the operations performed by the components illustrated inFIG. 1, are denoted with the same reference numerals as the referencenumerals of FIG. 1 and the structural and functional description ofthese components will be omitted.

The LD driver 200 includes a variable gain amplifier 20, a sample andhold circuit 22, an analog multiplexer 24, a differential amplifier 26,a gate 28, and a switch 30. The gate 28 determines an operating modesuch as a recording mode or a reproduction mode of an optical recordingand reproduction apparatus (not shown). Further, the gate 28 receiveschannel control signals such as peak control, bias control, and readcontrol, and determines the operating mode of the optical recording andreproduction apparatus. The operating mode of the optical recording andreproduction apparatus can be determined by applying a mode signal froma system control apparatus (not shown). In this case, an input pin (notshown) must be included in the conventional LD driver to receive themode signal. In order to avoid adding the input pin, the operating modeof the optical recording and reproduction apparatus may be determined bythe gate 28 from the channel control signals. The gate 28 determiningthe operating mode will now be described in detail.

The variable gain amplifier 20 amplifies an output signal MON-PD from amonitor diode (not shown) at different degrees of amplificationaccording to the operating mode of the optical recording andreproduction apparatus. The sample and hold circuit 22 samples and holdsthe signal output from the variable gain amplifier 20 and provides asampled and held signal as an inverted input to the differentialamplifier 26. The analog multiplexer 24 selects either a bias current ora read current according to the operating mode signal provided by thegate 28 and provides the selected current as a non-inverted input to thedifferential amplifier 26. The differential amplifier 26 outputs adifference between the inverted input and the non-inverted input. Theoutput of the differential amplifier 26 is applied to an adder 16. Theadder 16, in turn, outputs a driving signal, LD DRIVER_OUT to controlthe LD.

The switch 30 for selecting the LD to be driven is selected by an LDselection signal, SEL-LD, that is set according to the type of arecording medium determined by a system (not shown) at an initial stageof the operation of the optical recording and reproduction apparatus. Ahigh frequency modulator (HFM) 18 outputs different high frequencymodulation signals according to the LD to be driven.

The operation of the LD driver will now be described. Current such as,peak current, bias current, and read current, each of which correspondsto a power to be used by the LD such as a peak power level, a bias (orerase) power level, and a read power level, is applied to each of theswitches 10 a through 10 c. The power levels are continuously suppliedwhen the optical recording and reproduction apparatus operates and areturned on and off by the respective control signals such as peakcontrol, bias control, and read control.

FIG. 4A(a)–(h) illustrate waveforms showing a recording operation in aCD-Read Write (CD-RW). Specifically, FIG. 4A(a) illustrates a waveformof a non-return to zero inverter (NRZI) data. FIG. 4A(b) illustrates awaveform of a recording waveform (LD output signal). FIG. 4A(c)illustrates a waveform of a read control (active) signal. FIG. 4A(d)illustrates a waveform of a peak control signal. FIG. 4A(e) illustratesa waveform of a bias 1 control signal (erase power). FIG. 4A(f)illustrates a waveform of a bottom (base3) control signal (when fourchannels are used).

FIG. 4B(a)–(h) illustrate waveforms showing the recording operation in aDVD₁₃ RAM. Specifically, FIG. 4B(a) illustrates a waveform of an inputNRZI data. FIG. 4B(b) illustrates a waveform of a recording waveform (LDoutput signal). FIG. 4B(c) illustrates a waveform of a peak controlsignal (write level). FIG. 4B(d) illustrates a waveform of a bias1control signal (erase level). FIG. 4B(e) illustrates a waveform of abias 2 control signal (bottom level). FIG. 4B(f) illustrates a waveformof a bias2 control signal and bias3 control signal. FIG. 4B(g)illustrates a waveform of a bias3 control signal (cooling level). FIG.4B(h) illustrates a waveform of a read control signal (active).

It is possible to obtain a driving signal LD DRIVER_OUT having the samewaveform as the waveform of a recording pulse by combining controlsignals with each other. The driving signal LD DRIVER_OUT is applied tothe LD and the recording pulse of FIG. 4B(b) is obtained from the LD.Further, the LD has a temperature-dependent output characteristic asillustrated in FIG. 2. Namely, when the temperature of the LD increasesdue to an increase in temperature of the LD itself or an increase inexternal temperature, an optical output is reduced. The change in theoptical output according to the change in the temperature of the LD iscompensated by a closed loop including the variable gain amplifier 20,the sample and hold circuit 22, the differential amplifier 26, the adder16, and the LD (not shown).

The output level of the LD is detected by the monitor diode (not shown).The output signal MON-PD of the monitor diode is variably amplified bythe variable gain amplifier 20 according to the operating mode of theoptical recording and reproduction apparatus and is held by the sampleand hold circuit 22. Specifically, the gate 28 receives channel controlsignals, determines the mode of the optical recording and reproductionapparatus, and provides the mode signal showing the determined mode tothe variable gain amplifier 20, the sample and hold circuit 22, and theanalog multiplexer 24. The analog multiplexer 24 selects the biascurrent or the read current according to the operating mode of theoptical recording and reproduction apparatus and outputs the selectedcurrent. The differential amplifier 26 outputs the difference betweenthe output of the sample and hold circuit 22 and the output of theanalog multiplexer 24.

Table 1 illustrates the operating mode determining operation of the gate28.

TABLE 1 Read Erase Write control control control Mode Remarks 0 x xDisable LD driver disable 1 0 0 Reproduction HFM on 1 1 0 Recording HFMon and off 1 0 1 HFM off 1 1 1

As illustrated in Table 1, the gate 28 determines the optical recordingand reproduction apparatus to be in a recording and erase mode wheneither an erase control signal or a write control signal is active (inthe case of “1” in Table 1). In the recording and erase modes, the HFM18 may be on and/or off. The gate 28 determines the optical recordingand reproduction apparatus to be in a reproduction mode when the erasecontrol signal and the write control signal are inactive (in the case of“0” in Table 1) and a read control signal is active. In the reproductionmode, the HFM 18 is on. The gate 28 is determined to be in a disablemode, in which the LD must not be driven, when the read control signalis not active. As illustrated in Table 1, each operating mode isdetermined by the gate 28; accordingly, the operation characteristics ofthe variable gain amplifier 20, the sample and hold circuit 22, and theanalog amplifier 24 are determined by the gate 28.

In the case of the reading mode, a read gain is set by the variable gainamplifier 20, the sample and hold circuit 22 continuously orperiodically operates, and the analog multiplexer 24 selects a readcurrent. In the cases of the recording and erase mode, a write gain isset by the variable gain amplifier 20, the sample and hold circuit 22periodically operates, and the analog multiplexer 24 selects a bias (orerase) current. A sample and hold period is then selected from sectionsin which a bias control signal is active.

Table 2 illustrates the sampling operation of the sample and holdcircuit 22.

TABLE 2 Method of generating a Number sample and hold signal Remarks 0Output the bias control Obtain a necessary unchanged magnitude of signalfrom 1 Perform an AND operation each generated sample and on the biascontrol and the hold signal and can partially primary delay signal ofthe use the obtained magnitude bias control and output the of signal ANDoperation result 2 Perform an AND operation on the bias control and thesecondary delay signal of the bias control and output the AND operationresult 3 Perform an AND operation on the bias control and the tertiarydelay signal of the bias control and output the AND operation result

FIGS. 5( a)–(h) illustrate waveforms describing the sampling operationof the sample and hold circuit 22 in the LD driver 200 of FIG. 3according to Table 2. Specifically, FIG. 5( a) illustrates a waveform ofan example of inputting NRZI. FIG. 5( b) illustrates a waveform of bias1 control signal (example of high active). FIG. 5( c) illustrates awaveform of a primary delay signal of bias 1. FIG. 5( d) illustrates awaveform of a secondary delay signal of bias 1. FIG. 5( e) illustrates awaveform of a tertiary delay signal of bias 1. FIG. 5( f) illustrates awaveform of a sampling and holding signal 1 of bias 1. FIG. 5( g)illustrates a waveform of a sampling and holding signal 2 of bias 1.FIG. 5( h) illustrates a waveform of a sampling and holding signal 3 ofbias 1.

The sample and hold circuit 22 samples the bias control signal becausethe bias control signal can be easily sampled since the frequency of thebias control signal is lower than the frequency of the peak controlsignal or the read control signal. Further, the sample and hold circuit22 also samples the bias control signal because the amount of change ofthe bias control signal is less than the amount of change of the peakcontrol signal or the read control signal in an adaptive recordingmethod, in which the width or the rising or falling position of eachpulse that forms a multi train according to the length of an adjacentmark-space is shifted and recorded.

The width of the input NRZI data is different from the width of the biascontrol signal because the pulse width of the bias control signal variesaccording to a first pulse rising edge and a cooling pulse rising edge(this is also called an adaptive edge control). Also, a time delay unitof a signal obtained by delaying the bias control signal is shown to bethe same as the clock period of a recording medium. However, in order toimprove sampling precision degree, the time delay unit can be set to beshorter than the clock period of the recording medium. The switch 30selects the LD to be used according to the selection signal SEL-LD(e.g., an LD of 780 nm of a CD or an LD of 650 nm of a DVD). The processselecting the LD is performed during the initialization of the opticalrecording and reproduction apparatus.

The HFM 18 generates a high frequency modulation signal having differentfrequencies and magnitudes according to the type of LD to be used. Theoperation of the HFM 18 is controlled by the selection signal SEL-LD.Because the LD driver shown in FIG. 3 can control the power of the LDregardless of a run optimal power controller (ROPC), the apparatus maybe used separate from the ROPC or may be used in combination with theROPC. Here, the ROPC for driving current into the LD driver controlscurrent so that Vpp of a reproduction signal is uniform.

FIG. 6A and FIG. 6B are flowcharts illustrating an initializing methodand a driving method in accordance with an exemplary embodiment of thepresent invention. In FIG. 6A, operations 60 to 68 correspond to theinitializing method. In FIGS. 6A and 6B, operations 70 to 96 correspondto the driving method. At operations 70 to 96, the peak power level iscorrected or examined when the amount of change in the bias current ismore than a predetermined value.

At operation 50, memories are cleared, initial flag conditions are set,etc., as is well known in the art. At operation 60, the type of aninserted recording medium is monitored. Recording medium include a CD, aCD-RW, and a DVD. Because optical reflectivity varies according to therespective recording medium in general, the type of

recording medium is determined using the difference in the opticalreflectivity.

The initializing method performed at operations 60 to 68 is performed tobe suitable for the monitored type of recording medium. Namely, atoperation 62, the LD to be used is selected through the selection signalSEL-LD, driving potential and sampling timing information for the sampleand hold circuit 22 are set corresponding to the recording medium loadedinto the LD driver, and a monitoring boundary is set. The monitoringboundary means a boundary, within which bias driving potential or peakdriving potential does not need to be compensated for when the powerlevel of the laser signal output from the LD changes within a certainrange.

At operation 64, an optical pick-up is moved to the most innercircumference or the most outer circumference of the recording medium orfocus is moved up to the highest level or down to the lowest level.Operation 64 is a preparatory operation for testing the LD. At operation66, an LD test mode is performed. In the LD test mode, read recordingpower, erase recording power, and write recording power are output atuniform intervals during the initialization, the respective drivingpotentials are corrected by monitoring them, and the LD is tested formalfunction. The LD test mode may be used to test the LD duringinitialization; however, the LD test mode may be selectively performedduring the operation. Specifically, the LD test mode may be used fortesting or correcting the respective driving potentials.

The LD test mode may affect the information recorded in the recordingmedium during an LD testing operation. Therefore, in the LD test mode,the recorded information is protected by moving the optical pick-up tothe most inner circumference or the most outer circumference of therecording medium or moving the objective lens of the optical pick-up upor down to the highest level through a focus servo (not shown). It ispossible to minimize a time for testing the LD by moving up or down theobjective lens to the highest level rather than by moving the opticalpick-up to the most outer circumference or the most inner circumference.

At operation 68, the initializing method checks whether errors occur. Iferrors occur, the method returns to operation 62 and the LD isrepeatedly tested. If errors continuously occur, an interrupt isgenerated at operation 70 and the initializing method is terminated. Iferrors do not occur, at operation 74, the reproduction mode isperformed.

In the reproduction mode, a reproduction operation is performed througha search or seek operation. At operation 76, a data reproduction isperformed. At operation 80, when the recording mode is determined, thebias current is stored. At operation 82, a most recent bias current isdetected. At operation 84, the stored bias current is compared with themost recent bias current and it is determined whether the differencebetween the stored bias current and the most recent bias currentdeviates from the monitoring boundary which is set at operation 62.

If the bias current is within the monitoring boundary, then, atoperation 86 a search operation or seek operation is performed. Atoperation 88, the recording mode operation records data and, atoperation 90, data is reproduced or verified.

Because LD driver 200 of FIG. 3 performs an auto laser power control(ALPC) operation on the basis of the bias current during a recording orerasing operation as shown in Table 2, the peak power can becompensated, if necessary, by periodically controlling the peak current.Therefore, when the bias current slightly deviates from the monitoringboundary, the amount of peak current compensation errors is negligible.Specifically, when the slopes of the bias current and the monitoringboundary are identical or almost identical to each other, the peakcurrent compensation errors need not be compensated.

When the detected bias current deviates from the monitoring boundary,that is, when the amount of change in the bias current is more than apredetermined value, the peak power is corrected or checked. Themonitoring boundary varies according to the LDs. The allowance degree ofa search range is higher in a higher output LD.

At operation 84, if the bias current is not within the monitoringboundary, at operation 92, the optical pick-up is moved to the mostinner circumference or the most outer circumference of the recordingmedium or the objective lens is moved up or down to the highest levelthrough focus servo. At operation 94, the amount of correction iscalculated according to a previously written look-up table or apredetermined calculation. At operation 96, the peak (write) power iscorrected by applying the calculated amount of correction. The recordingmode operation proceeds to operation 80 and the bias current is updated.

As mentioned above, according to the LD driver 200 in accordance to thepresent invention, it is possible to prevent the occurrence of amis-operation due to electromagnetic wave interference generated duringan interface between the LD driver and the ALPC circuit, which areseparated from each other like in the conventional technology becausethe ALPC circuit is loaded into the LD driver.

Also, because a plurality of LDs may be driven by one LD driver, thelower compatibility and share of media occur. According to theinitializing method in accordance with the present invention, the LDdriver is initialized corresponding to a recording medium in the opticalrecording and reproduction apparatus for driving a plurality of LDs byone LD driver. According to the method of driving the LD, in accordanceto the present invention, the change in the output power of the LD isadaptively compensated.

While this invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade thereto without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A method of compensating for a bias driving potential of an LD driveraccording to a change in a power level of a laser signal from an LD in arecording mode, comprising: storing the bias driving potential;detecting a change in a bias power level in the laser signal;compensating the bias driving potential according to the detected changein the bias power level; and determining whether the detected change inthe bias power level within a predetermined monitoring boundary, whereinthe bias driving potential is not compensated when the detected changeis within a predetermined monitoring boundary, and the bias drivingpotential is compensated, according to the detected change in the biaspower level, when the detected change is not within the predeterminedmonitoring boundary.
 2. The method as recited in claim 1, furthercomprising compensating a peak driving potential that sets a peak powerlevel of the LD corresponding the detected change in the bias powerlevel when the detected change in the bias power level is not within thepredetermined monitoring boundary.
 3. A laser diode driving method fordriving a laser diode (LD) which outputs a bias power level and a peakpower level corresponding to a bias driving potential and a peak drivingpotential respectively, the method comprising: detecting the bias powerlevel; calculating a difference between the detected bias power leveland a saved bias power level; and correcting the peak power level basedon the difference when the difference exceeds a predetermined monitoringboundary, wherein a variance in temperature output characteristics ofthe LD is corrected.
 4. The method as recited in claim 3, furthercomprising: updating the saved bias power level using the detected biaspower level when the difference exceeds a predetermined monitoringboundary.
 5. The method as recited in claim 3, further comprisingcorrecting the peak power level based on a difference between acurrently-sampled bias power level and a previously-sampled bias powerlevel, wherein the detecting the bias power level is done insynchronization with a bias control signal which controls the biasdriving potential.
 6. The method as recited in claim 3, wherein themethod is performed at the begining of a recording operation.